It is often necessary or desirable to vaporize a cryogenic liquid (i.e., to bring about vaporization of a cryogenic liquid to a vaporized state). For example, and though a wide variety of applications exist for liquid vaporization, it is often necessary or desirable to vaporize liquid natural gas (LNG) so that it can be handled and distributed as a fuel source.
Many vaporization systems operate with burners in order to produce the necessary vaporization heat. For example, evaporators of the submerged combustion type comprise a water bath in which a flue gas tube of a gas burner is installed as well as an exchanger tube bundle for the vaporization of the liquefied gas. The gas burner discharges the combustion flue gases into the water bath, which heat the water and provide the heat for the vaporization of a liquefied gas that flows through the tube bundle. Such vaporization systems are provided, for example, by T-Thermal Company, a division of Selas Fluid Processing Corporation, under the registered trademark SUB-X.
Evaporators of this type are reliable and of compact size, but they may become expensive to operate. For example, in order to reduce emissions of nitrogen oxide (NOx) from such systems, a current practice utilizes a gaseous fuel burner in combination with water injection to reduce NOx emissions. In such systems, NOx emissions can be reduced to approximately 30 ppmvd, corrected to 3 volume percent oxygen (dry basis).
Further reduction of NOx emissions may require post combustion catalytic treatment. For example, a catalytic treatment system may be located at the outlet of a submerged liquid bath. Such treatment utilizes a portion of the burner exhaust to reheat the gases that are exiting the liquid bath, so as to reduce the moisture content of the gases before they enter the post combustion catalytic system. The corresponding use of this portion of the burner exhaust can, however, reduce the energy efficiency of the system, since this portion of the burner gases are not used to heat the cryogenic fluid.
Accordingly, there remains a need for an improved method and system for cryogenic liquid vaporization.